JP3336854B2 - Catalyst deterioration determination device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for determining deterioration of a three-way catalyst for purifying exhaust gas of an internal combustion engine. The present invention relates to a catalyst deterioration determination device for an internal combustion engine that can prevent erroneous determination even when the oxygen release capacity exceeds a limit.

[0002]

BACKGROUND ART unburned components exhaust gas contains discharged from an internal combustion engine for an automobile (HC, CO, NO _X) in order to purify, oxidation and N of HC and CO in the engine exhaust system
It is common to equip the three-way catalyst performs O _X of the reduction at the same time. Here, in order to maintain the purification performance of the three-way catalyst, it is necessary to control the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine to the stoichiometric air-fuel ratio. The air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine is controlled to the target air-fuel ratio by feedback-controlling the output of a sensor that detects the concentration of residual oxygen in the exhaust gas.

[0003] However, at the upstream side of the three-way catalyst, for example, at the junction of the exhaust manifold, variations in sensor output due to insufficient mixing of exhaust gas discharged from each cylinder, exhaust gas and internal combustion engine Air-fuel ratio control accuracy may decrease due to deterioration of the sensor due to heat. In order to solve this problem, a sensor is also installed downstream of the three-way catalyst, and in addition to main feedback control based on the output of the upstream sensor, sub-feedback control based on the output of the downstream sensor is introduced to improve the air-fuel ratio control accuracy. Improved double sensor systems are already in practical use.

However, even in a double sensor system,
If the purification performance of the three-way catalyst is deteriorated, that is, if the oxygen storage effect of the three-way catalyst is reduced, it is unavoidable that the air-fuel ratio control accuracy is reduced. A catalyst deterioration judging device for judging the degree of deterioration of a source catalyst has been proposed (JP-A-5-989).
No. 48).

That is, when the three-way catalyst is not deteriorated, it has an oxygen storage effect of adsorbing oxygen when the property of the exhaust gas is rich and releasing it when the property of the exhaust gas is lean. Since the reversal cycle of the downstream sensor output is sufficiently longer than the reversal cycle of the above, the trajectory length of the downstream sensor output is shorter than the trajectory length of the upstream sensor output, and the three-way catalyst is normal. Is determined.

On the other hand, when the three-way catalyst has deteriorated, the oxygen storage effect decreases and the number of reversals of the downstream sensor output increases. Accordingly, the trajectory length of the downstream sensor output is substantially equal to the trajectory length of the upstream sensor output, and it is determined that the three-way catalyst has deteriorated.

[0007]

However, even when the three-way catalyst is normal, if the balance of the oxygen balance, that is, the balance between the ability to adsorb and release oxygen, exceeds the limit, the output of the downstream sensor is inverted. As a result, the three-way catalyst may be erroneously determined to be deteriorated due to a long trajectory length.

FIG. 2 is an explanatory view of the above problem.
(A) shows the output of the downstream sensor, and (B) shows the oxygen balance of three primary colors. That downstream sensor the time t ₂ before is rich, reversed from time t ₂ from the rich to lean in t _3, from time t ₃ to t ₅ is maintained lean, the lean from time t ₅ at t ₆ inverted to the rich, from the time t ₆ to t ₈ to maintain the rich, inverted from the time t ₈ from rich to lean at t _9.

Accordingly the three-way catalyst adsorbs oxygen at time t ₃ before from time t ₃ to t ₆ releases oxygen, from time t ₆ to t ₉ adsorbs oxygen, at the time t ₉ after Releases oxygen. Therefore adsorbed acid <br/> elementary charge up to time t ₃ is the three-way catalyst gradually increases, gradually increasing the oxygen release amount of the three-way catalyst is from time t ₃ toward t _6, a period from time t ₆ to t ₉ Means that the adsorbed oxygen amount of the three-way catalyst gradually increases, and the time t
After ₉ the oxygen release gradually increases.

However, the amount of adsorbed oxygen of the three-way catalyst and the amount of oxygen released from the three-way catalyst have a limit (indicated by a dashed line in (b)).
From ₁ to t _3, from time t ₄ to t _6, and time t
In ₇ to t ₉ misclassification risk occurs.
The present invention has been made in view of the above-mentioned problems, and has been made in consideration of the above-described problems, and the catalyst balance of an internal combustion engine that can prevent erroneous determination even when the oxygen balance of a three-way catalyst, that is, the oxygen adsorption capacity and the oxygen release capacity exceed their limits, It is an object to provide a discriminating device.

[0011]

FIG. 1 is a basic block diagram of an apparatus for judging catalyst deterioration of an internal combustion engine according to the present invention. An apparatus for determining catalyst deterioration of an internal combustion engine according to claim 1 is provided upstream of a three-way catalyst for purifying exhaust gas installed in an exhaust system of the internal combustion engine and upstream of detecting a concentration of a specific component in exhaust gas. Side air-fuel ratio sensor 11 and a downstream oxygen sensor 12 provided on the downstream side for detecting the concentration of a specific component in the exhaust gas.
Air-fuel ratio feedback control means 13 for controlling the amount of fuel supplied to the internal combustion engine in accordance with at least the output of upstream air-fuel ratio sensor 11;
A deterioration determining means 14 for determining the deterioration of the three-way catalyst based on the output of No. 2 ;
Of the three-way catalyst based on the integral of the fuel deviation
Oxygen balance estimating means 15 for estimating the oxygen balance of the three-way catalyst when the oxygen balance in the three-way catalyst exceeds the limit value of the oxygen adsorption capacity or the limit value of the oxygen release capacity of the three-way catalyst. A deterioration determination stopping means for stopping the determination of deterioration of the three-way catalyst by the deterioration determining means.

[0012] According to the present device , based on the integral value of the fuel deviation amount,
If the parameter indicating the estimated oxygen balance of the three-way catalyst exceeds a predetermined upper and lower limit value, the possibility of erroneous determination is determined and the deterioration determination is stopped. In the catalyst deterioration determining apparatus for an internal combustion engine according to the second aspect , the oxygen balance estimating means includes a basic fuel amount necessary for controlling the air-fuel ratio to a stoichiometric air-fuel ratio and an actual fuel amount calculated by the air-fuel ratio feedback control means. A fuel deviation amount calculating means for calculating a fuel deviation amount which is a difference between the two, a reversal detecting means for detecting reversal of the output of the downstream oxygen sensor, and a reversal detecting means for detecting reversal of the output of the downstream oxygen sensor. Until the reversal of the output of the downstream oxygen sensor is detected by the reversal detection means, the integrated value of the fuel deviation calculated by the fuel deviation value calculation means is integrated, and the oxygen balance in the three-way catalyst is estimated based on the integrated value. And a fuel deviation integrated value integrating means.

According to the present device, the oxygen balance in the three-way catalyst is estimated based on the integrated value obtained by integrating the fuel deviation amount from the time when the downstream oxygen sensor is inverted to the time when the downstream oxygen sensor is inverted again. Claim
In the catalyst deterioration judging device for an internal combustion engine according to the third aspect , the deterioration judging suspending means may be configured to determine whether the fuel deviation value integrated by the fuel deviation amount accumulating value accumulating means exceeds the predetermined upper and lower limit values even if the integrated value of the fuel deviation value exceeds a predetermined upper and lower limit value. Until the predetermined period of time elapses after the output of the oxygen sensor is inverted, suspension of the determination of deterioration of the three-way catalyst is suppressed.

According to the present apparatus, even if the integrated value of the fuel deviation exceeds the predetermined upper and lower limit values, the deterioration determination is allowed as long as the output of the downstream oxygen sensor does not start reversing. According to a fourth aspect of the present invention, there is provided a catalyst deterioration determining apparatus for an internal combustion engine, wherein the reversal detecting means sets a hysteresis characteristic between a threshold value for determining a rich to lean reversal and a threshold value for determining a lean to rich reversal. Having.

According to this device, the hysteresis characteristic is applied to the inversion of the output of the downstream oxygen sensor, that is, the detection of the inversion from rich to lean or from lean to rich. The catalyst deterioration determination device for an internal combustion engine according to claim 5 is
The deterioration judging means judges the deterioration of the three-way catalyst based on the trajectory length of the output of the upstream air-fuel ratio sensor and the trajectory length of the output of the downstream oxygen sensor.

According to the present apparatus, the deterioration is determined based on the ratio of the trajectory lengths of the outputs of the upstream and downstream sensors.
According to a sixth aspect of the present invention, there is provided the internal combustion engine catalyst deterioration determining apparatus, wherein the deterioration determining means is configured to perform the determination based on the number of times that the integrated value of the fuel deviation value integrated by the fuel deviation amount integrated value integrating means exceeds a predetermined upper and lower limit value. Thus, the deterioration of the three-way catalyst is determined.

According to the present device, the deterioration determination is performed based on the number of times the integrated value of the fuel deviation value exceeds the upper and lower limit values.
An apparatus for determining catalyst deterioration of an internal combustion engine according to claim 7 is provided upstream of a three-way catalyst for purifying exhaust gas installed in an exhaust system of the internal combustion engine and upstream of detecting a concentration of a specific component in exhaust gas. A downstream oxygen sensor provided on the downstream side and a concentration of a specific component in exhaust gas provided on the downstream side;
An air-fuel ratio correction coefficient for correcting the amount of fuel supplied to the internal combustion engine in accordance with at least the output of the upstream oxygen sensor and an air-conditioning device for calculating a learning value for correcting a secular change of equipment related to fuel amount control. Fuel-fuel ratio feedback control means, deterioration determination means for determining deterioration of the three-way catalyst based on at least the output of the downstream oxygen sensor, and deviation between the air-fuel ratio correction coefficient calculated by the air-fuel ratio feedback control means and the air-fuel ratio learning value Oxygen balance estimating means for estimating the oxygen balance in the three-way catalyst according to the integral value of the three-way catalyst, and deterioration determining means when the oxygen balance in the three-way catalyst exceeds a predetermined threshold value by the oxygen balance estimating means. And a means for stopping the determination of deterioration of the three-way catalyst.

According to this device, in the case of a so-called double oxygen sensor system, the oxygen balance of the three-way catalyst is estimated based on the integral value of the difference between the air-fuel ratio correction coefficient and the air-fuel ratio learning value.

[0019]

FIG. 3 is a block diagram of an embodiment of a catalyst deterioration determining apparatus according to the present invention. An air flow meter 33 is provided in an intake passage 32 of an internal combustion engine body 31. The air flow meter 33 measures the amount of intake air, and outputs a voltage signal proportional to the amount of intake air by using a built-in potentiometer. This voltage signal is supplied to the A / D converter 301 with a built-in multiplexer of the control unit 30.

The distributor 34 outputs, for example, a reference position detecting sensor 35 which converts the crank angle into 720 ° pulses for reference position detection and a crank angle which outputs a crank position detecting pulse every 30 °. A crank position detection sensor 36 is provided. These pulses are supplied to the input / output interface 30 of the control unit 30.
2 and the crank position detection pulse is CP
It is also supplied to the interrupt terminal of U303.

A fuel injection valve 3 for injecting fuel supplied from a fuel supply system for each cylinder is provided in the intake passage 32.
7 is also installed. The water jacket 38 of the internal combustion engine body 31 is provided with a temperature sensor 39 for detecting the cooling water temperature THW.
A voltage proportional to W is supplied to the control unit 30 using the multiplexer A
/ D converter 301.

The exhaust manifold 311 of the internal combustion engine 31
Downstream, toxic components HC, CO and NO in the exhaust gas
_xConverter containing a three-way catalyst that simultaneously purifies air
312 are provided. Exhaust manifold 311 immediately
The upstream side of the catalytic converter 312 has an upstream air-fuel ratio sensor.
The exhaust pipe 3 on the downstream side of the catalytic converter 312
14 has a downstream O _TwoA sensor 315 is provided. Up
The flow-side air-fuel ratio sensor 313 detects the residual oxygen concentration in the exhaust gas.
A substantially proportional output signal is generated, and the downstream O_TwoSensor 31
5 generates a binary signal according to the residual oxygen concentration in the exhaust gas
A / D converter 30 with built-in multiplexer of control unit 30
Feed to 1.

The control unit 12 is, for example, a microcomputer system, and includes an A / D converter 30 with a built-in multiplexer.
1, the input / output interface 302, the CPU 303, the ROM 304, the RAM 305, the battery backup memory B-RAM 306, the clock 307, and the like. Further, a down counter 308, a flip-flop 309, and a drive circuit 310 are circuits for driving the fuel injection valve 37. The fuel injection time TAU is calculated in a routine described later, and the down counter 308 and the flip-flop 309 are set. The drive circuit 310 starts energizing the fuel injection valve 37. Down counter 308
Is incremented by the clock signal,
When "1" is output from the carry-out terminal of the down counter 308, the flip-flop 309 is reset, and the drive circuit 310 stops energizing the fuel injection valve 37. Therefore, a fuel amount corresponding to the fuel injection amount FI is supplied to the combustion chamber of the internal combustion engine 10.

Further, an alarm 316 is connected to the input / output interface 302, and operates when the control unit 30 determines that the three-way catalyst has deteriorated to call the driver's attention. Intake air amount Q detected by air flow meter 33 and cooling water temperature TH detected by temperature sensor 39
W is fetched by an A / D conversion routine executed every predetermined time and stored in a predetermined address of the RAM 305.
That is, the intake air amount Q and the cooling water temperature THW stored in the RAM 305 are updated every predetermined time.

The rotation speed Ne is calculated by an interruption of the crank position detection sensor 36 every 30 ° CA, and is calculated by RA
It is stored at a predetermined address of M305. FIG. 4 is a flowchart of a deterioration determination main routine executed by the control unit 30. The flag operation processing is performed in step 41, the oxygen balance calculation processing is performed in step 42, and the deterioration determination control processing is performed in step 43. Will be described later.

[0026] Figure 5 is a flow chart of a flag operation process executed in the step 41, the downstream O ₂ sensor 3
The object of the present invention is to provide a hysteresis characteristic in order to stabilize the inversion detection of the 15 outputs. That is, the output of the downstream O ₂ sensor 315 is likely to be inverted near the stoichiometric air-fuel ratio. However, when there is no hysteresis characteristic, if the parameter representing the oxygen balance of the three-way catalyst is frequently cleared by the inversion, the deterioration determination is always performed. This is to prevent the erroneous determination from easily occurring due to the execution.

In step 411, it is determined whether or not the output OXS of the downstream O ₂ sensor 315 is equal to or greater than the rich threshold value KOXR.
Then, the process proceeds to step S2, where the downstream air-fuel ratio flag XOXSR is set to "1", and the process is terminated. If a negative determination is made in step 412, the process proceeds to step 413, where the downstream O ₂ sensor 31
It is determined whether the output OXS of No. 5 is equal to or smaller than the lean side threshold value KOXL. If the determination is affirmative, the downstream air-fuel ratio flag XOXSR is set to "0" in step 414, and this processing ends. If a negative determination is made in step 413, this process ends directly.

FIG. 6 is a hysteresis characteristic diagram of the inversion detection. When the output OXS of the downstream O ₂ sensor 315 is equal to or larger than the rich threshold value KOXR, the downstream air-fuel ratio flag XOXSR is set to “1”. Conversely, when the output OXS of the downstream O ₂ sensor 315 is less than or equal to the lean threshold KOXL, the downstream air-fuel ratio flag XOXSR is set to “0”.

When the output is inverted from rich to lean, the downstream air-fuel ratio flag XOX is maintained until the output OXS of the downstream O ₂ sensor 315 reaches the lean threshold KOXL.
SR is maintained at "1", the downstream air-fuel ratio flag XOXSR up if inverted from lean to rich output OXS the downstream O ₂ sensor 315 reaches the rich side threshold KOXR is maintained at "0" Is done.

FIG. 7 is a flowchart of the oxygen balance calculation process executed in step 42, which estimates the oxygen absorption degree and oxygen release degree of the three-way catalyst, that is, the oxygen balance, based on the integral value of the fuel deviation amount described later. It is. That is,
If the property of the exhaust gas detected by the downstream O ₂ sensor 315 is rich, the air-fuel ratio control reduces the fuel amount from the fuel amount corresponding to the stoichiometric air-fuel ratio in order to control the exhaust gas property lean. At this time, the three-way catalyst continues to absorb residual oxygen in the exhaust gas. That is, the integral value of the fuel deviation amount can be considered to represent the amount of oxygen adsorbed on the three-way catalyst.

Conversely, if the properties of the exhaust gas detected by the downstream O ₂ sensor 315 are lean, the air-fuel ratio control increases the fuel amount from the fuel amount corresponding to the stoichiometric air-fuel ratio in order to control the exhaust gas properties rich. . At this time, the three-way catalyst continues to release the absorbed oxygen. That is, since the integral of the fuel deviation can be considered to represent the amount of oxygen released by the three-way catalyst, the oxygen balance of the three-way catalyst can be estimated from the integral of the fuel deviation. .

In step 421, it is determined whether or not the downstream air-fuel ratio flag XOXSR has been inverted. Step 421
, That is, the downstream air-fuel ratio flag XOX
When SR is inverted, in step 422, the fuel deviation integral amount FDINT is reset to "0", and step 42 is executed.
Proceed to 3. When a negative determination is made in step 421,
That is, if the downstream air-fuel ratio flag XOXSR is not inverted, the process directly proceeds to step 423.

At step 423, XOXSR = ""
1 "and FD ₀ <0, that is, whether the downstream air-fuel ratio is rich and the fuel is injected so as to correct the air-fuel ratio to lean. When the determination in step 423 is affirmative, If there is no contradiction between the downstream air-fuel ratio detected by the downstream O ₂ sensor 315 and the fuel injection amount, the process proceeds to step 424, and the fuel deviation integrated value FD is calculated by the following equation.
INT is added up, and this process ends.

FDINT = FDINT + FD _{0 If a} negative determination is made in step 423, step 425 is reached.
To check if XOXSR = 0 and FD ₀ > 0,
That is, it is determined whether the downstream air-fuel ratio is lean and the fuel is being injected so as to correct the air-fuel ratio richly.

When an affirmative determination is made in step 425, that is, when there is no contradiction between the downstream air-fuel ratio detected by the downstream O ₂ sensor 315 and the fuel injection amount, the routine proceeds to step 424. If a negative determination is made in step 425, this process is directly terminated. FIG. 8 is a flowchart of the deterioration determination control process executed in step 43. In step 431, the fuel deviation integrated value FDINT is set to the lower limit value KD.
It is determined whether the value is between FCL and the upper limit value KDFCR.

The fuel deviation integrated value FDINT is equal to the integrated lower limit value K.
If it is between DFCL and the accumulated upper limit value KDFCR, an affirmative determination is made in step 431, the flow proceeds to step 432 to count the monitoring time, the counter CNT is decremented, and the flow proceeds to step 436. Fuel deviation integrated value FDIN
T is determined that the oxygen absorbing capability or oxygen release capability of the three-way catalyst when not between the lower limit KDFCL and the upper limit value KDFCR exceeds the limit, the downstream side in step 43 3 and 43 4 are negative decision is made at step 431 It is determined whether the output OXS of the O ₂ sensor 315 is equal to or larger than the sensor output upper limit KOXa or equal to or smaller than the sensor output lower limit KOXb.

When the output OXS of the downstream O ₂ sensor 315 is not less than the sensor output upper limit KOXa or not more than the sensor output lower limit KOXb, it is determined that the oxygen absorption capacity or oxygen release capacity of the three-way catalyst has exceeded the limit. It is assumed that there is still room in practice and steps 433 and 434
Is determined to be affirmative, the routine proceeds to step 432, and the counter CNT
Is decremented and the routine proceeds to step 436. This is a measure for increasing the chance of discrimination by utilizing the margin since the threshold for judging the limit of the oxygen absorption capacity or the oxygen release capacity of the three-way catalyst is usually set with a margin. .

When the oxygen absorption capacity or the oxygen release capacity of the three-way catalyst exceeds the limit and the output OXS of the downstream O ₂ sensor 315 starts the reversing operation, step 431:
A negative determination is made in all of the steps 433 and 434, and the counter CNT is set to a predetermined value KTDL to stop the determination of the deterioration of the three- way catalyst, and a step 436 is performed.
Proceed to.

In step 436, it is determined whether or not the count value of the counter CNT is "0". When the determination is affirmative, that is, when a predetermined monitoring time has elapsed, an erroneous determination is made in the determination of deterioration of the three-way catalyst. At step 437, a deterioration determination flag X
The MCAT is set to "1" and the process ends. Conversely, when a negative determination is made in step 436, that is, after it is determined that the oxygen absorption capacity or oxygen release capacity of the three-way catalyst has exceeded the limit, the output OXS of the downstream O ₂ sensor 315 is changed to the sensor output upper limit KOXa or the sensor output. Lower limit KO
If it falls within Xb, it is determined that there is a risk of erroneous determination, and the deterioration determination flag XMCAT is set to "" in step 438.
In step 438, the deterioration determination flag XMCAT is set to "0" to stop the deterioration determination even if the monitoring time has not elapsed.
Set to "0".

FIG. 9 is a flow chart of a routine for determining the deterioration of the three-way catalyst, which is executed by the control unit 30. In step 91, it is determined whether or not the deterioration determination flag XMCAT is "1". Terminates this routine directly without executing the deterioration determination. When an affirmative determination is made in step 91, the process proceeds to step 92 to execute the deterioration determination, and it is determined whether or not the monitoring condition for deterioration determination of the three-way catalyst is satisfied.

The deterioration of the three-way catalyst is determined when all of the following conditions are satisfied. (1) The air-fuel ratio feedback control by the upstream air-fuel ratio sensor 313 is being executed. The details of this condition will be described later. (2) The air-fuel ratio feedback control by the downstream O ₂ sensor 315 is being executed. The details of this condition will be described later. (3) The internal combustion engine load is equal to or more than a predetermined value.

Therefore, when any of the above conditions (1) to (3) is not satisfied, a negative determination is made in step 92 and the routine is directly terminated without performing the deterioration determination. Conversely, when all of the above conditions (1) to (3) are satisfied, an affirmative determination is made in step 92 and a step 9 is executed.
Proceed to 3. In step 93, a trajectory length calculation process is executed, which will be described later in detail.

[0043] increments the monitoring time counter CTIME for counting the deterioration determining monitoring time at step 94, determines whether the count value of the monitoring time counter CTIME is the predetermined value C ₀ or more in step 95. If a negative determination is made in Step 9 5, that is, when a predetermined monitor time has not passed this routine is directly terminated.

[0044] When an affirmative determination is made in Step 9 5 Conversely,
That is, when the predetermined monitoring time has elapsed, step 96 is executed.
Then, a deterioration determination process is executed, and this routine ends. The details of the deterioration determination process will be described later. FIG. 10 is a flowchart of the trajectory length calculation processing executed in step 93. In step 931, the upstream air-fuel ratio sensor 31
3 is converted to an output VAFH for calculating a trajectory length.

VAFH = f (VAF) In step 932, the upstream air-fuel ratio sensor 313 is calculated by the following equation.
Is calculated based on the trajectory length calculation output VAFH. LVAFH = LVAFH + | VAFH−VAFHO | Here, VAFHO is a previously calculated output for calculating the trajectory length of the upstream air-fuel ratio sensor 313.

Next, at step 933, the downstream O
Calculating the downstream O ₂ output trajectory length LVOS based on the output OXS _two sensors 315. LVOS = LVOS + | OXS − OXSO | where OXSO is the output of the downstream air-fuel ratio sensor 315 calculated last time. Next, in step 934, in preparation for the next execution, the previously calculated value is updated as follows, and this processing ends.

VAFHO ← VAFH VOSO ← VOS FIG. 11 is a flowchart of the deterioration judging process executed in step 96. In step 961, the deterioration judging process of the three-way catalyst is performed based on the output locus length of the upstream air-fuel ratio sensor. Calculate the threshold _Lref .

L _ref = f (LVAFH) In step 962, the downstream O ₂ output locus length LVOS
Is greater than or _equal to the threshold value _Lref, that is, whether the three-way catalyst has deteriorated. When an affirmative determination is made in step 962, that is, when it is determined that the three-way catalyst has deteriorated, the alarm flag ALMCC is determined in step 963.
Is set to "1", an alarm is activated in step 964, and the flow advances to step 966.

On the other hand, if a negative determination is made in step 962, that is, if it is determined that the three-way catalyst has not deteriorated, an alarm flag ALMCC is set in step 965.
Is set to "0", and the routine proceeds to step 966. Step 9
At 66, the alarm flag ALMCC is set to B-RAM3.
06. This is a procedure for reading out the determination result at the time of repair and inspection.

[0050] Further provided in the next processing at step 967, resets the monitoring time counter CTIME, the upstream air-fuel ratio sensor output trajectory length LVAFH and downstream O ₂ output trajectory length LVOS and the processing ends. FIG. 12 is a flowchart of a target in-cylinder fuel amount calculation routine executed by the control unit 30, which is executed as an interruption process at every predetermined crank angle.

[0051] In step 121, the previous cylinder air amount calculated in this routine MC _i and target cylinder fuel amount FCR _i a (i = 0~n-1) 1 at a time migration. This is a process for calculating the current in-cylinder air amount MC ₀ and the target in-cylinder fuel amount FCR ₀ in this execution. In step 122, the internal combustion engine speed Ne and the intake air amount Q stored in the RAM 305 are fetched.

[0052] In step 123, calculates the cylinder air amount MC ₀ the current as a function of engine speed Ne and the intake air amount Q. MC ₀ = MC (Ne, Q) Further, at step 124, the current target in-cylinder fuel amount FCR
_0, i.e., in the current cylinder air amount MC ₀ the amount of fuel required for making the air-fuel ratio the stoichiometric air-fuel ratio is calculated by the following equation and this routine is terminated.

FCR ₀ = MC ₀ / AFT where AFT is the stoichiometric air-fuel ratio (14.7). FIG.
Is a flowchart of a main air-fuel ratio feedback control routine executed by the control unit 30, which is executed as an interrupt process at regular time intervals of, for example, 4 milliseconds.

In step 131, it is determined whether a feedback control condition by the upstream air-fuel ratio sensor 313 is satisfied. That is, when all of the following conditions are satisfied, the feedback control by the upstream air-fuel ratio sensor 313 is permitted. (1) The cooling water temperature is equal to or higher than a predetermined temperature. (2) The internal combustion engine is not starting. (3) The fuel is not being increased, such as when starting. (4) The output of the upstream air-fuel ratio sensor has been inverted at least once. (5) The fuel is not being cut.

If all of the above conditions are satisfied and the feedback control by the upstream air-fuel ratio sensor 313 is permitted, an affirmative determination is made in step 131 and a step 13 is performed.
2 and the fuel deviation FD _i (i
= 1 to n) by one. This is to calculate the current fuel deviation amount FD ₀ in the current calculation. Next, at step 133, the output VA of the upstream air-fuel ratio sensor 313
F is corrected by the following equation by a voltage correction amount DV calculated in a sub air-fuel ratio feedback control routine described later.

VAF = VAF + DV The output VAF of the upstream air-fuel ratio sensor 313 after further correction.
Is used to calculate the current actual air-fuel ratio ABF. ABF = g (VAF) in step 135, n times before the cylinder air amount MC _n calculated in this routine, the target cylinder fuel amount FCR _n
And the current fuel deviation FD ₀ based on the current actual air-fuel ratio ABF is calculated by the following equation.

FD ₀ = MC _n / ABF−FCR _n Here, the in-cylinder air amount MC _n and the target in-cylinder fuel amount F calculated by executing n times before to obtain the current fuel deviation amount FD _0.
CR _n is used for the upstream air-fuel ratio sensor 31 from the cylinder.
This is for correcting the exhaust gas transport delay time up to 3. Finally, in step 136, the fuel correction amount DF is calculated based on the following equation, and this routine ends.

DF = k _fp * FD ₀ + k _fs * ΣFD _i where k _fp is a proportional gain and k _fs is an integral gain. If any of the conditions (1) to (5) is not satisfied, a negative determination is made in step 131 and the routine proceeds to step 137, where the air-fuel ratio correction amount DF is set to "0", and this routine ends.

FIG. 14 is a flowchart of a sub air-fuel ratio feedback control routine executed by the control unit 30. The sub air-fuel ratio feedback control routine is executed as an interrupt process at predetermined time intervals longer than the execution time, for example, every second. You. In step 141, the downstream O ₂
It is determined whether the feedback control condition by the sensor 315 is satisfied.

That is, when all the same conditions as the main air-fuel ratio feedback control are satisfied, the feedback control by the downstream O ₂ sensor 315 is permitted. That is, when the feedback control by the downstream O ₂ sensor 315 is allowed, the process proceeds to step 142 is affirmative determination is made in step 141, the voltage deviation VD _i calculated previously previous
(I = 1 to n) are moved one by one. This is for calculating the current voltage fuel deviation VD ₀ in this calculation.

Next, at step 143, the output OXS of the downstream O ₂ sensor 315 and the target downstream O ₂ sensor output V
The current voltage deviation VD ₀ from the OST is calculated by the following equation. VD ₀ = OXS - VOST finally calculates voltage correction amount DV based on the following equation at step 144 the routine is terminated.

DV = k _vp * VD ₀ + k _vs * ΣVD _i where k _vp is a proportional gain and k _vs is an integral gain. If any one of the downstream O ₂ sensor feedback control conditions is not satisfied, a negative determination is made in step 141 and the routine proceeds to step 145, where the voltage correction amount DV is set to “0”, and this routine ends.

FIG. 15 is a flowchart of a fuel injection control routine for controlling the amount of fuel injected into the internal combustion engine, which is executed at predetermined crank angles. In step 151, the target in-cylinder fuel amount calculation routine calculates
Target in-cylinder fuel amount FCR ₀ The fuel injection amount FI is calculated by correcting with the air-fuel ratio correction amount DF.

FI = α * FCR ₀ + DF + β where α and β are determined according to other operating parameters
It is a correction coefficient. In step 152 , the fuel injection amount FI is set in the down counter 308 via the input / output interface 302, and the routine ends. FIG.
Is an explanatory diagram of the operation of the above embodiment, in which the horizontal axis represents time, and each waveform represents the output V of the upstream air-fuel ratio sensor 313 from above.
AF, the output OXS of the downstream O ₂ sensor 315, and the fuel deviation integrated value FDINT.

That is, before time t _1, the fuel deviation integrated value FD
INT is between the upper limit value KDFCR and the lower limit value KDFCL, and the deterioration determination is allowed on the assumption that the oxygen adsorption capacity of the three-way catalyst has not reached the limit. At time t ₁ , the fuel deviation integrated value FDINT becomes equal to or lower than the lower limit value KDFCL, and it is determined that the oxygen adsorption capacity of the three-way catalyst has reached the limit. However, before time t ₂ , the output OXS of the downstream O ₂ sensor 315 is The discrimination is permitted by assuming that it is not less than the upper limit value KOXa and the reversal has not been started, thereby increasing the chance of discrimination. Whereas the time t ₂ thereafter determines as being the misclassification risk for outputting OXS the downstream O ₂ sensor 315 starts reversing is stopped.

From time t ₃ to time t ₄ , the determination is allowed assuming that the oxygen release capacity of the three-way catalyst has not reached the limit. At time t ₄ , the fuel deviation integrated value FDINT becomes the upper limit K
Although it is determined that the oxygen release capacity of the three-way catalyst has reached the limit because of the DFCR or more, the output OXS of the downstream O ₂ sensor 315 is less than or equal to the sensor lower limit value KOXb and has not started reversing before time t _5. And the discrimination is allowed to increase the discrimination opportunity. On the other hand, the time t ₅ after that determination as there is misclassification risk for outputting OXS the downstream O ₂ sensor 315 starts reversing is stopped.

[0067] In the above embodiment has implemented the deterioration determination of the three-way catalyst based on the locus length of the output of the upstream air-fuel ratio sensor 313 and the downstream O ₂ sensor 315, but the output is the downstream O ₂ sensor 315 It is also possible to determine the deterioration of the three-way catalyst based on the number of times the fuel deviation integral value has exceeded the lower limit value KDFCL and the upper limit value KDFCR between the inversions and the next inversion.

FIG. 17 is a flowchart of a second deterioration determination execution routine for performing the deterioration determination by the above-described method.
Is executed in place of the trajectory length calculation processing of FIG. That is, in step 1701, the downstream air-fuel ratio flag XOXS operated in the flag operation process of FIG.
It is determined whether R has been inverted.

When an affirmative determination is made in step 1701, that is, when the downstream air-fuel ratio flag XOXSR is inverted, the routine proceeds to step 1702, where the deterioration determination flag XMCAT is set to "
1 ", that is, whether deterioration determination is permitted. When an affirmative determination is made in step 1702, that is, when deterioration determination is permitted, in step 1703, the fuel deviation integrated value FDINT is set to the upper limit value KDFCR. In step 1704, the fuel deviation amount integrated value FDIN
It is determined whether T is equal to or smaller than the lower limit value KDFCL.

The fuel deviation integrated value FDINT is equal to the upper limit value KD.
If it is out of the FCR or the lower limit KDFCL, an affirmative determination is made in step 1703 or 1704.
In step 1705, the abnormality counter CJFCAT is incremented, and the flow advances to step 1707 . Conversely, the fuel deviation integrated value FDINT is equal to the upper limit value KDFCR and the lower limit value KDFC.
If it is within the range of L, steps 1703 and 17
In step 1706 , a negative determination is made, and in step 1706, the normal counter CJSCAT is incremented, and the flow advances to step 1707.

After resetting the fuel deviation integral value FDINT in step 1707, the count value of the normal counter CJSCAT is reset to a predetermined value C in step 1708.
It is determined whether or not s is greater than s. If an affirmative determination is made in step 1708, the flow advances to step 1709 to reset the alarm flag ALMCC to "0" and terminate this routine.

[0072] proceeds to step 1710 when a negative determination in step 1708, determines whether the count value of the abnormal counter CJFCAT becomes a predetermined or greater than a predetermined value Cf. If an affirmative determination is made in step 1710, the process proceeds to step 1711, where the alarm flag ALMCC is set to "1", an alarm is activated in step 1712, and this routine ends.

In the above embodiment, the upstream side sensor 3
13 is an air-fuel ratio sensor (linear sensor), a downstream sensor 3
Although 15 is an O ₂ sensor, the downstream sensor 315 may be an air-fuel ratio sensor. However, in this case, it is necessary to convert the downstream-side O ₂ sensor output VOS into a trajectory calculation output VOSH in the trajectory length calculation processing of FIG. Further, in the above embodiment, the upstream sensor 1
Reference numeral 33 denotes an air-fuel ratio sensor (linear sensor), but the present invention can also be applied to a so-called double O ₂ sensor system in which the upstream sensor 133 is also an O ₂ sensor.

However, in this case, the output of the O ₂ sensor is not proportional to the amount of residual oxygen in the exhaust gas, and the fuel injection amount is
_{(2) Since the} output is not directly proportional to the sensor output, the oxygen balance of the three-way catalyst cannot be estimated based on the integrated value of the fuel deviation amount. So using the integral value of the deviation between the air-fuel ratio correction coefficient and the air-fuel ratio learned value as a means for estimating the oxygen balance of the three-way catalyst.

[0075] Figure 18 is a flow chart of a second oxygen balance calculation process in place of the oxygen balance calculation process shown in FIG. 7 is executed when the double O ₂ sensor system, the downstream air-fuel ratio flag in step 181 It is determined whether XOXSR has been inverted. When an affirmative determination is made in step 181, that is, when the downstream air-fuel ratio flag XOXSR is inverted, the routine proceeds to step 182, where the air-fuel ratio deviation integrated value FAFI
NT is reset and the routine proceeds to step 183. On the other hand, when a negative determination is made in step 181, the process directly proceeds to step 183.

In step 183, the air-fuel ratio deviation DFAF is calculated by the following equation as the difference between the air-fuel ratio correction coefficient FAF and the air-fuel ratio learning value FG. The air-fuel ratio correction coefficient FAF and the air-fuel ratio learning value FG will be described later. DFAF = FAF-FG In step 184, it is determined whether XOXSR = 1 and DFAF <0, and if affirmative, step 18
In step 5, the air-fuel ratio deviation integrated value FAFINT is updated by the following equation.

FAFINT = FAFINT + DFAF When a negative determination is made in step 184, step 186 is executed.
It is determined whether XOXSR = 0 and DFAF> 0, and if affirmatively determined, step 18 is executed.
At 5, the air-fuel ratio deviation integrated value FAFINT is updated. If a negative determination is made in step 186, this process is directly terminated.

FIG. 19 shows a first example of the double O ₂ sensor system which is executed to calculate the air-fuel ratio correction coefficient FAF and the air-fuel ratio learning value FG in place of the main air-fuel ratio feedback control routine shown in FIG. FIG. 9 is a flowchart of an air-fuel ratio correction coefficient calculation routine, wherein at predetermined time intervals,
For example, it is executed every 4 milliseconds. In step 191, it is determined whether a feedback control condition by the upstream O ₂ sensor 313 is satisfied.

These conditions are as described in the main air-fuel ratio feedback control routine shown in FIG.
All these conditions are satisfied and the upstream O ₂ sensor 3
When the feedback control by 13 is permissible, an affirmative determination is made in step 191 and the process proceeds to step 192 where the output V ₁ of the upstream O ₂ sensor 313 is read. Subsequently, in step 193, the first delay processing is performed in step 194.
Then, the air-fuel ratio correction coefficient calculation processing is executed, and this routine ends.

The upstream O_TwoFee by sensor 313
If any of the feedback control conditions are not satisfied,
A negative determination is made at step 191 and the routine proceeds to step 195, where
By setting the fuel ratio correction coefficient FAF to "1.0"
End FIG. 20 is a flowchart showing the processing executed in step 193.
1 is a flowchart of delay processing of Step 19
3a upstream O_TwoOutput V of sensor 313₁Is the first comparison
Voltage V _1R(For example, 0.45 V) or less, that is, upstream
Side O_TwoThe air-fuel ratio detected by the sensor 313 is lean
Is determined.

When a positive determination is made in step 193a,
That is, when the air-fuel ratio detected by the upstream O ₂ sensor 313 is lean, the process proceeds to step 193b, and it is determined whether the count value of the first delay counter CDLY1 is positive. When an affirmative determination is made in step 193b, the first delay counter CDLY1 is determined in step 193c.
Is reset and the routine proceeds to step 193d. If a negative determination is made in step 193b, the process proceeds directly to step 193d.
Proceed to.

At step 193d, the first delay counter CDLY1 is decremented, and at step 193e, it is determined whether the count value of the first delay counter CDLY1 is equal to or less than the first lean delay time TDL1. When an affirmative determination is made in step 193e, i.e. when the output V ₁ of the upstream O ₂ sensor 313 has elapsed first lean delay time TDL1 From the above inverted from rich to lean,
In step 193f, the first delay counter CDLY1
Is set to the first lean delay time TDL1, and step 1
At 93g, the first air-fuel ratio flag F1 is set to "0", and this processing ends. If a negative determination is made in step 193e, this process is directly terminated.

[0083] Note that the first lean delay time TDL1 is a delay time for the output V ₁ of the upstream O ₂ sensor 131 is to delay the inversion of the first air-fuel ratio flag F1 when inverted from rich to lean , Defined as negative time. When a negative determination is made in step 193a, that is, when the air-fuel ratio detected by the upstream O ₂ sensor 313 is rich, the process proceeds to step 193h, and it is determined whether the count value of the first delay counter CDLY1 is negative. .

When an affirmative determination is made in step 193h, the first delay counter CDLY1 is set in step 193i.
Is reset and the routine proceeds to step 193j. If a negative determination is made in step 193h, step 193j is entered directly.
Proceed to. In step 193j, the first delay counter C
DLY1 is incremented, and in step 193k, the first
It is determined whether the count value of the delay counter CDLY1 is less than or equal to the first rich delay time TDR1.

When a positive determination is made in step 193k,
That is, if the first rich delay time TDR1 or more has elapsed since the output V _{1 of the} upstream O ₂ sensor 313 was inverted from lean to rich, in step 193l, the first delay counter CDLY1 is set to the first rich delay time TDR1. And at step 193m, the first air-fuel ratio flag F1 is set to "
1 "and the process ends. Step 19
If a negative determination is made in 3k, this process is directly terminated.

[0086] Note that the first rich delay time TDR1 is a delay time for the output V ₁ of the upstream O ₂ sensor 313 is to delay the inversion of the first air-fuel ratio flag F1 when inverted from lean to rich , Defined as positive time. FIG. 21 is a flowchart of the air-fuel ratio correction coefficient calculation process executed in step 194.
It is determined at a whether the first air-fuel ratio flag F1 has been inverted.

When an affirmative determination is made in step 194a,
That is, when the first air-fuel ratio flag F1 is inverted, it is determined in step 194b whether the first air-fuel ratio flag F1 is "0". When an affirmative determination is made in step 194b, that is, when the first air-fuel ratio flag F1 is inverted from rich to lean, the air-fuel ratio correction coefficient F
Step 1 by increasing AF in a skipping manner by the following equation
Proceed to 94h.

FAF ← FAF + RSR When a negative determination is made in step 194b, that is, when the first air-fuel ratio flag F1 is inverted from lean to rich,
In step 194d, the air-fuel ratio correction coefficient FAF is skipped by the following equation, and the process proceeds to step 194h. FAF ← FAF-RSL When a negative determination is made in step 194a, that is, when the first air-fuel ratio flag F1 is not inverted, step 1 is executed.
At 94e, it is determined whether the first air-fuel ratio flag F1 is "0".

When an affirmative decision is made in step 194e,
That is, when the first air-fuel ratio flag F1 continues to be lean, the air-fuel ratio correction coefficient FAF is slightly increased by the following equation at step 194f, and the routine proceeds to step 194h. FAF ← FAF + KIR When a negative determination is made in step 194e, that is, when the first air-fuel ratio flag F1 continues to be rich, in step 194g, the air-fuel ratio correction coefficient FAF is slightly reduced by the following equation, and the process proceeds to step 194h. .

FAF ← FAF-KIL Note that KIL and KIR are integral constants, and are set to values sufficiently smaller than the skip constants RSR and RSL. In step 194h, the air-fuel ratio correction coefficient FAF is limited by a maximum value (for example, 1.2) and a minimum value (for example, 0.8).

This is a measure for preventing the air-fuel ratio from becoming over-lean or over-rich even when the air-fuel ratio correction coefficient FAF becomes too large or too small for some reason. Further, at step 194i, a learning process is executed, and this process ends. FIG. 22 is a flowchart of the learning process executed in step 194i. In step 221, it is determined whether the first air-fuel ratio flag F1 has been inverted. When a negative determination is made, that is, when the first air-fuel ratio flag F1 is determined. If it has not been inverted, this process ends directly.

When the determination in step 221 is affirmative, that is, when the first air-fuel ratio flag F1 is inverted, step 2 is executed.
The program then proceeds to 22 to calculate a moving average value FAFAV of the air-fuel ratio correction coefficient FAF by the following equation. FAFAV = {(m-1) * FAFAV + FAF} / m Here, m is the number of samples used for calculating the moving average.

In steps 223 and 224, the moving average value FAFAV is equal to or more than a predetermined upper limit value UL (for example, 1.005) or a lower limit value LL (for example, 0.99).
5) It is determined whether or not the following conditions are satisfied. If the determination is affirmative in step 223 or step 224, the fuel injection system devices such as the upstream and downstream O ₂ sensors 313 and 315 and the fuel injection valve 37 have changed over time. The learning value of the air-fuel ratio is updated.

That is, when the determination in step 223 is affirmative, the learning value FG is updated by the following equation in step 225, and this processing ends. FG = FG + ΔG Here, ΔG is a constant (for example, 0.002). When an affirmative determination is made in step 224, the learning value FG is updated by the following equation in step 226, and this processing ends.

FG = FG-ΔG If a negative determination is made in step 224 , it is determined that no aging has occurred in the fuel injection system equipment, and this process is directly terminated without updating the learning value FG. FIG. 23 shows double O ₂
15 is a flowchart of a second air-fuel ratio correction coefficient calculation routine that is executed in place of the sub-air-fuel ratio feedback control routine shown in FIG. 14 in the case of the sensor system, and is executed every predetermined time, for example, every second.

At step 231, it is determined whether the feedback control condition by the downstream O ₂ sensor 315 is satisfied. This condition is the same as the feedback condition in the sub air-fuel ratio feedback control routine shown in FIG.
_{When the} feedback control by the _two sensors 315 is permitted, an affirmative determination is made in step 231 and step 232 is performed.
Proceeds to read the output V ₂ of the downstream O ₂ sensor 315.

Subsequently, the second delay processing is executed in step 233, and the control constant calculation processing is executed in step 234, and this routine is ended. If any of the above conditions is not satisfied, a negative determination is made in step 231, the rich skip constant RSR is set to the initial value RSR ₀ in step 235, and the lean skip constant RSL is set to the initial value RSL ₀ in step 236. Set and end this routine.

FIG. 24 is a flow chart showing the second processing executed in step 233.
Is a flowchart of the delay processing of step 233.
a downstream O_TwoOutput V of sensor 315_TwoIs the second comparative
Pressure V _2R(For example, 0.55 V) or less, that is,
O_TwoThe air-fuel ratio detected by the sensor 315 is lean
It is determined whether there is. Where upstream or below the catalytic converter
O on the downstream side_TwoSensor output characteristics and deterioration degree are different
In consideration of the second comparison voltage V_2RIs the first comparison voltage
V_1RIt is common to set higher.

When a positive determination is made in step 233a,
That is, when the air-fuel ratio detected by the downstream O ₂ sensor 315 is lean, the process proceeds to step 233b, and it is determined whether the count value of the second delay counter CDLY2 is positive. If an affirmative determination is made in step 233b, then in step 233c the second delay counter CDLY2
Is reset and the routine proceeds to step 233d. If a negative determination is made in step 233b, the process directly goes to step 233d.
Proceed to.

In step 233d, the second delay counter CDLY2 is decremented, and in step 233e, it is determined whether the count value of the second delay counter CDLY2 is equal to or less than the second lean delay time TDL2. When an affirmative determination is made in step 233e, that is, when the output V _{2 of the} downstream O ₂ sensor 315 is inverted from rich to lean and the second lean delay time TDL2 or more has elapsed,
In step 233f, the second delay counter CDLY2
Is set to the second lean delay time TDL2, and step 2
At 33g, the second air-fuel ratio flag F2 is set to "0", and this processing ends. If a negative determination is made in step 233e, this process is directly terminated.

The second lean delay time TDL2 is a delay time for delaying the inversion of the second air-fuel ratio flag F2 when the output V ₂ of the downstream O ₂ sensor 315 is inverted from rich to lean. , Defined as negative time. When a negative determination is made in step 233a, that is, when the air-fuel ratio detected by the downstream O ₂ sensor 315 is rich, the process proceeds to step 233h, and it is determined whether the count value of the second delay counter CDLY2 is negative. .

If the determination in step 233h is affirmative, the flow proceeds to step 233i where the second delay counter CDLY2 is set.
Is reset and the routine proceeds to step 233j. If a negative determination is made in step 233h, step 233j is entered directly.
Proceed to. In step 233j, the second delay counter C
DLY2 is incremented, and the second
It is determined whether the count value of the delay counter CDLY2 is equal to or less than the second rich delay time TDR2.

When the determination in step 233k is affirmative,
That is, when the output V _{2 of the} downstream O ₂ sensor 315 is inverted from lean to rich and the second rich delay time TDR2 or more has elapsed, the second delay counter CDLY2 is set to the second rich delay time TDR2 in step 233l. And the second air-fuel ratio flag F2 is set to "" in step 233m.
The processing is terminated by setting the value to "1". Step 23
If a negative determination is made in 3k, this process is directly terminated.

Note that the second rich delay time TDR2 is a delay time for delaying the inversion of the second air-fuel ratio flag F2 when the output V ₂ of the downstream O ₂ sensor 315 is inverted from lean to rich. , Defined as positive time. FIG. 25 is a flowchart of the control constant calculation process executed in step 234. In step 234a, it is determined whether the second air-fuel ratio flag F2 is "0".

When the determination in step 234a is affirmative,
That is, if the air-fuel ratio detected by the downstream O ₂ sensor 315 is lean, the process proceeds to step 234b, and the rich skip constant RSR is increased by a predetermined amount ΔRS according to the following equation. RSR = RSR + ΔRS When the rich skip constant RSR is equal to or larger than the predetermined maximum value MAX in steps 234c and 234d, the maximum value is limited by the maximum value MAX.

At step 234e, the lean skip constant R
SL is reduced by a predetermined amount ΔRS according to the following equation. RSL = RSL -DerutaRS Li in step 234f and 234 g - when Nsukippu constant RSL is equal to or less than a predetermined minimum value MIN is limited by a minimum value MIN and the processing ends.

When a negative determination is made in step 234a,
That is, if the air-fuel ratio detected by the downstream O ₂ sensor 315 is rich, the process proceeds to step 234h, and the rich skip constant RSR is reduced by a predetermined amount ΔRS by the following equation. RSR = RSR-ΔRS If the rich skip constant RSR is equal to or smaller than the predetermined minimum value MIN in steps 234i and 234j, the restriction is made with the minimum value MIN.

At step 234k, the lean skip constant R
SL is increased by a predetermined amount ΔRS according to the following equation. RSR = RSR + ΔRS If the lean skip constant RSL is equal to or larger than the predetermined maximum value MAX in steps 234l and 234m, the process is terminated by limiting the lean skip constant RSL to the maximum value MAX.

FIG. 26 is a flowchart of a second fuel injection control routine that replaces the fuel injection control routine shown in FIG. 15 in the case of the double O ₂ sensor system, and is executed at every predetermined crank angle. In step 261
The target in-cylinder fuel amount FCR ₀ is calculated by subtracting the air-fuel ratio
The fuel injection amount TI is obtained by correcting with the learning value .

TI = α * FCR ₀ (FAF + FG) + β where α and beta via the output interface 302 of the fuel injection amount FI in constant and Step 26 2 down counter 308
And ends this routine.

In the above embodiment, the skip constant is changed based on the output of the downstream O ₂ sensor. However, other control constants, that is, the integral constants KIR and KIL, the first delay times TDR and TDL, or the first At least one of the comparison voltages V _1R may be changed. It is also possible to introduce the second air-fuel ratio correction coefficient FAF2 based on the output of the downstream O ₂ sensor.

[0112]

According to the first aspect of the present invention, the actual in-cylinder fuel injection amount and the target in-cylinder fuel injection amount are determined.
When it is determined that the oxygen balance in the three-way catalyst calculated based on the fuel deviation, which is the difference in fuel amount, has exceeded the limit, the occurrence of erroneous determination is suppressed by stopping the three-way catalyst deterioration determination. Becomes possible. According to the catalyst deterioration determining device for an internal combustion engine according to claim 2, when the upstream-side air-fuel ratio sensor is a linear sensor can be estimated oxygen balance in the three-way catalyst by the integral value of the fuel deviation Become.

According to the catalyst deterioration determining apparatus for an internal combustion engine according to the third aspect , even if the integral value of the fuel deviation exceeds a predetermined upper and lower limit value, deterioration determination is performed as long as the output of the downstream oxygen sensor does not start to be inverted. , It is possible to suppress a decrease in the opportunity for deterioration determination. According to the catalyst deterioration determining apparatus for an internal combustion engine according to the fourth aspect , by making the detection of the inversion of the output of the downstream oxygen sensor have hysteresis, erroneous determination caused by frequently resetting the integral value of the fuel deviation amount is provided. Is prevented.

According to the catalyst deterioration determining apparatus for an internal combustion engine according to the fifth aspect, it is possible to determine the degree of deterioration of the three-way catalyst based on the ratio of the trajectory lengths of the outputs of the upstream and downstream air-fuel ratio sensors. According to the catalyst deterioration determination device for an internal combustion engine according to the sixth aspect , it is possible to determine the degree of deterioration of the three-way catalyst based on the number of times that the integral value of the fuel deviation exceeds a predetermined upper and lower limit.

According to the catalyst deterioration judging device for an internal combustion engine according to the seventh aspect , even when the upstream air-fuel ratio sensor is an oxygen sensor, when it is determined that the oxygen balance of the three-way catalyst has exceeded the limit, the three-way catalyst is determined. Canceling the catalyst deterioration determination makes it possible to suppress the occurrence of erroneous determination.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of a catalyst deterioration determination device for an internal combustion engine according to the present invention.

FIG. 2 is an explanatory diagram of a problem.

FIG. 3 is a configuration diagram of an embodiment of a catalyst deterioration determination device for an internal combustion engine according to the present invention.

FIG. 4 is a flowchart of a deterioration determination main routine.

FIG. 5 is a flowchart of a flag operation process.

FIG. 6 is a hysteresis characteristic diagram.

FIG. 7 is a flowchart of an oxygen balance calculation process.

FIG. 8 is a flowchart of a deterioration determination process.

FIG. 9 is a flowchart of a deterioration determination execution routine.

FIG. 10 is a flowchart of a trajectory length calculation process.

FIG. 11 is a flowchart of a deterioration determination process.

FIG. 12 is a flowchart of a target in-cylinder fuel amount calculation routine.

FIG. 13 is a flowchart of a main air-fuel ratio feedback control routine.

FIG. 14 is a flowchart of a sub air-fuel ratio feedback control routine.

FIG. 15 is a flowchart of a fuel injection control routine.

FIG. 16 is a diagram illustrating the operation of the embodiment.

FIG. 17 is a flowchart of a second deterioration determination execution routine.

FIG. 18 is a flowchart of a second oxygen balance calculation process.

FIG. 19 is a flowchart of a first air-fuel ratio correction coefficient calculation routine.

FIG. 20 is a flowchart of a first delay process.

FIG. 21 is a flowchart of an air-fuel ratio correction coefficient calculation process.

FIG. 22 is a flowchart of a learning process.

FIG. 23 is a flowchart of a second air-fuel ratio correction coefficient calculation routine.

FIG. 24 is a flowchart of a second delay process.

FIG. 25 is a flowchart of a control constant calculation process.

FIG. 26 is a flowchart of a second fuel injection control routine.

[Explanation of symbols]

31 ... engine 33 ... air flow meter 34 ... distributor 35 ... reference position detection sensor 36 ... crank angle detection sensor 30 ... control unit 312 ... catalytic converter 313 ... upstream air-fuel ratio sensor 315 ... downstream O ₂ sensor

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-5-280402 (JP, A) JP-A-5-163989 (JP, A) JP-A-7-151002 (JP, A) JP-A-7-151 34860 (JP, A) JP-A-6-213048 (JP, A) JP-A-9-41954 (JP, A) JP-A-8-144744 (JP, A) JP-B-7-26580 (JP, B2) Patent Publication 7-18368 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) F01N 3/08-3/38 F01N 9/00-11/00 F02D 41/00-41 / 40 F02D 43/00-45/00

Claims (7)

(57) [Claims] 1. An upstream air-fuel ratio sensor provided upstream of a three-way catalyst for exhaust gas purification installed in an exhaust system of an internal combustion engine for detecting the concentration of a specific component in exhaust gas, and provided downstream. A downstream oxygen sensor that detects the concentration of a specific component in the exhaust gas, and an air-fuel ratio feedback control unit that controls an amount of fuel supplied to the internal combustion engine at least according to an output of the upstream air-fuel ratio sensor. A deterioration determining means for determining deterioration of the three-way catalyst based on the output of the downstream oxygen sensor, and a deviation between the actual in-cylinder injected fuel amount and the target in-cylinder fuel amount.
The oxygen balance in the three-way catalyst is calculated based on the integrated value of the fuel deviation.
And oxygen balance estimating means for estimating the oxygen balance of the three-way catalyst by the oxygen balance estimating means,
A deterioration determination stopping means for stopping the deterioration determination of the three-way catalyst by the deterioration determining means when the limit value of the oxygen adsorption capacity or the limit value of the oxygen release capacity of the three-way catalyst is exceeded. Discriminator. 2. The method according to claim 1, wherein the oxygen balance estimating means determines a basic fuel amount necessary for controlling the air-fuel ratio to a stoichiometric air-fuel ratio.
Actual fuel calculated by the air-fuel ratio feedback control means
Fuel deviation amount calculator that calculates the fuel deviation amount that is the difference from the amount
Stage and inversion detection for detecting inversion of the output of the downstream oxygen sensor
Means for detecting the output of the downstream oxygen sensor by the inversion detecting means.
After the inversion is detected, the downstream
Until the re-inversion of the output of the side oxygen sensor is detected.
Integrates the integrated value of the fuel deviation calculated by the deviation calculation means
And, based on the integrated value, estimate the oxygen balance in the three-way catalyst.
2. A fuel deviation amount integrated value integrating means.
The catalyst deterioration determination device for an internal combustion engine according to claim 1. 3. The fuel cell system according to claim 2, wherein the deterioration determination suspending means includes a fuel deviation integrated by the fuel deviation integrated value integrating means.
When the integrated value of the difference value exceeds a predetermined upper / lower limit
Is also predetermined after the output of the downstream oxygen sensor is inverted.
Until the specified time has elapsed, the three-way catalyst
Catalyst for an internal combustion engine according to claim 2 also of a is to suppress stop
Medium deterioration determination device. 4. The method according to claim 1, wherein said inversion detecting means is rich to lean.
Threshold to judge reversal to lean and return from lean to rich
Has hysteresis characteristics between the threshold value for judging
An apparatus for determining catalyst deterioration of an internal combustion engine according to claim 2. 5. The air-fuel ratio on the upstream side according to claim 1 , wherein
Of the trajectory length of the sensor output and the output of the downstream oxygen sensor
This is to determine the deterioration of the three-way catalyst based on the trajectory length.
The catalyst deterioration determining device for an internal combustion engine according to claim 1. 6. A fuel cell system according to claim 1 , wherein said deterioration determining means includes a fuel deviation quantity product.
The integrated value of the fuel deviation value integrated by the
Three-way catalyst based on the number of times exceeding the specified upper and lower limits
3. The internal combustion engine according to claim 2, wherein the deterioration of the engine is determined.
Catalyst deterioration determination device. 7. Exhaust gas installed in an exhaust system of an internal combustion engine
Provided upstream of the three-way catalyst for purification
Upstream oxygen sensor and downstream for detecting the concentration of specific components
On the side to detect the concentration of specific components in exhaust gas
A flow-side oxygen sensor and an internal combustion engine at least according to the output of the upstream-side oxygen sensor
-Fuel ratio corrector for correcting the amount of fuel supplied to the engine
Over time for equipment related to quantity and fuel quantity control.
Air-fuel ratio feedback that calculates the air-fuel ratio learning value to correct
And a three-way control based on at least the output of the downstream oxygen sensor.
Deterioration determination means for determining catalyst deterioration, and air-fuel ratio calculated by the air-fuel ratio feedback control means
In the three-way catalyst according to the integral value of the deviation between the correction coefficient and the learning value
Oxygen balance estimating means for estimating the oxygen balance of the catalyst, and the oxygen balance in the three-way catalyst is predicted by the oxygen balance estimating means.
The deterioration determining means when a predetermined threshold value is exceeded.
Determination stop means for stopping the three-way catalyst deterioration determination by
And a catalyst deterioration determination device for an internal combustion engine, comprising: